The relationship between hyperoxaluria and urinary calculus disease is being studied in intestinal bypass patients and in animals with segmental bowel resections. A registry of the 635 previously bypasses patients has been established and has been used to identify a group of oxalate stone formers. Pre- and postoperative studies have been performed and are being performed to help distinguish those conditions and findings associated with stone formation. A reliable method for the determination of serum and urinary oxalate has been established, and is being used to quantitate changes seen after intestinal bypass. Methods of quantitating the urinary crystal formation of stone formers and non-stone formers have been applied to the pre- and postoperative patients in an attempt to develop a means of preoperative identification of stone formers. In addition, the quantitative urinary crystal production identification of stone formers. In addition, the therapeutic measures designed to reduce stone formation in post-bypass patients. An in vivo animal assay for the experimental testing of anti-calculus therapy has also been developed. In this assay, a constant urinary production of oxalate crystals is established. Therapeutic agents are then administered to the preparation and changes in crystal production recorded. In the next 12 months therapeutic measures directed toward the reduction of oxalate crystal excretion, and thus to the prevention of urinary stone formation, both those previously reported and those suggested from this present study, will be applied to human registry patients.